Re: hyperthreaded cpu still an issue in 8.4?

On Tue, 21 Jul 2009, Doug Hunley wrote:

> Just wondering is the issue referenced in
> http://archives.postgresql.org/pgsql-performance/2005-11/msg00415.php
> is still present in 8.4 or if some tunable (or other) made the use of
> hyperthreading a non-issue. We're looking to upgrade our servers soon
> for performance reasons and am trying to determine if more cpus (no
> HT) or less cpus (with HT) are the way to go.

If you're talking about the hyperthreading in the latest Intel Nehalem
processors, I've been seeing great PostgreSQL performance from those.
The kind of weird behavior the old generation hyperthreading designs had
seems gone. You can see at
http://archives.postgresql.org/message-id/alpine.GSO.2.01.0907222158050.16713@westnet.com
that I've cleared 90K TPS on a 16 core system (2 quad-core hyperthreaded
processors) running a small test using lots of parallel SELECTs. That
would not be possible if there were HT spinlock problems still around.
There have been both PostgreSQL scaling improvments and hardware
improvements since the 2005 messages you saw there that have combined to
clear up the issues there. While true cores would still be better if
everything else were equal, it rarely is, and I wouldn't hestitate to jump
on Intel's bandwagon right now.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD